This invention relates to robot machines and in particular to robot hands of a robot machine.
A robot hand has been proposed in which two sets of workpiece grasping units are provided for the fore end of an arm for the purpose of decreasing the number of opeations of the hands for loading or unloading the workpiece on or from a machine tool capable of machining continuously with the robot hand. More particularly, while one grasping unit of the robot hand utilized to unload a workpiece secured to the machine tool by a chuck, for example, is made to be idle, the other grasping unit is actuated to grasp another workpiece to be subsequently loaded. As the robot hand approaches a chuck, the idle grasping unit is aligned with the workpiece and, then, the fingers of that grasping unit are operated to grasp the workpiece. When the chuck releases the workpiece, the other grasping unit is coaxial with the chuck and, then, the jaws of the chuck are closed to securely load the new workpiece on the machine tool. Then, the workpiece removed from the machine tool is grasped by the idle grasping unit. The hand, which has finished supplying the new workpiece, is returned to a predetermined position. Thus, when compared with a robot machine having only one hand, it is possible to save one conveyance operation corresponding to one reciprocating motion, during each operation described above.
However, during the above-described operations, when the center of the chuck is shifted from alignment with the center of one grasping unit to alignment with the center of the other grasping unit, the realignment has occurred through motion of the arm. In such a case, depending on the relative position of the grasping units, it is necessary to move the hand in the vertical direction or to reverse the motion of the entire hand.
In this case, since the weight of the arm acts as a load on a member to be manipulated some operating power is lost and quick operation is impaired. Moreover, vibrations are liable to be induced, making it difficult to accurately align centers.